1. Field of the Invention
This invention has particular application to metal treating systems in which a coating metal is applied to a metal strip by the well known hot-dip process. An accepted method of treating a zinc coated steel strip, for example, is to utilize resistance heating after the strip leaves the zinc bath so as to effect complete alloying of the zinc and steel base to form a "galvanealed" type product. High strip temperatures at the point of first roll contact above the pot cause a severe roll pick-up hazard. Use of a graphite film on the first roll above the zinc pot prevents adherence of coating metal particles to the surface of such roll; this film also reduces friction between the strip and roll surface without disturbing electrical continuity between the strip and the roll for resistance heating.
2. Description of the Prior Art
No patentability search has been conducted to determine whether graphite films have been used in the manner contemplated by this invention. It is known, however, that when coating metal picks up on the roll surface to a certain point, the coated sheet is subjected to damage which may result in rejected material. It has been the practice in the past, therefore, to mechanically clean the roll from time to time by the use of wire brushes or by scraping. This, however, seems to result in more and more roll scraping being needed. Such frequent roll scrapings are inherently difficult and inconvenient. It has also been known to use internal water cooling of the roll to cut down pickup but this has resulted in strip distortion. Other coatings evaluated were either nonconductive or not effective. Thus, for example, tower rolls have been glass coated, ceramic coated, chromium coated or sprayed externally with water, all with but limited success.